1. Field of the Invention
The present invention relates to a camera having a shutter and particularly an electronic still camera having a focal-plane shutter, such as an interchangeable lens type single lens reflex camera.
2. Description of the Related Art
In an electronic still camera having a focal-plane shutter, such as a single lens reflex camera, an image pickup element (image sensor) is arranged behind the focal-plane shutter. Upon photographing, the focal-plane shutter is opened so that object light transmitted through a photographing lens (image pickup optical system) can be received by an image pickup element. FIG. 2 shows main components of a known single lens reflex camera type of electronic still camera.
The object light transmitted through a photographing lens (not shown) is reflected by a quick return mirror 13, is transmitted through a focusing screen 15 which is located in a position optically equivalent to an image forming surface position IP, is converged by a condenser lens 17, is reflected by a pentagonal prism 19, and is emitted from an eyepiece 21. A user views an erect real image of an object formed on the focusing screen 15 through the eyepiece 21, the pentagonal prism 19 and the condenser lens 17. Upon exposure, the quick return mirror 13 is moved up, and the focal-plane shutter curtain 23 is opened. The object image formed by the photographing lens (not shown) is projected onto an image pickup surface 103 of an image pickup element 101.
In such an interchangeable lens type single lens reflex camera, the image pickup element 101 is provided in an internal space of a camera body 11. However, foreign matter such as dust can enter the camera body during attachment or detachment of the lens. Therefore, there is a possibility that foreign matter sticks to a surface of an optical element which is located closer to the object (subject) than the image pickup element 101 in the light path, for example, a low-pass filter 105. If foreign matter sticks to the surface of the low-pass filter 105, a clear image of the foreign matter is projected onto the image pickup surface 103, thus resulting in deteriorated image quality.